Hydrogels produced by swelling a polymer compound such as polyhydroxyethyl methacrylate in a water-based solvent have elasticity similar to matter in living bodies, and impart superior wearing feel; therefore, they are used for ophthalmic lenses such as contact lenses. Examples of typical hydrogels used in an ophthalmic lens include silicone hydrogels prepared by copolymerizing a silicone monomer (or macromer) with a hydrophilic monomer.
However, waste products in the lacrimal fluid and bacteria in the air are likely to attach to the ophthalmic lens in which such a hydrogel is used, and thus proliferation of bacteria in hydrogel systems are likely to occur, whereby eye diseases and the like may be developed. To cope with such disadvantages, cleanliness of the lens can be maintained by periodically executing disinfection such as boiling. However, such a treatment is laborious, and the disinfecting effect does not persist for a long period of time. In addition, a method of immersing in a cleaning and preservative solution for contact lenses, referred to as “multipurpose solution”, containing an antiseptic component was proposed, and has become broadly prevalent. However, in addition to the disadvantages similar to those described above, wearing of contact lenses results in disadvantages of inferior effect of suppressing bacterial infection during wearing due to bleeding out of the antibacterial component together with the lacrimal fluid. Therefore, development of a technique of imparting an antibacterial effect to the ophthalmic lens per se has been in progress.
Also, an ophthalmic lens in which a hydrogel is used generally has a high moisture content, and the moisture gradually volatilizes during the lens is kept wearing, accompanied by absorption of the lacrimal fluid into the hydrogel. Therefore, feeling of dryness is likely to be provided, and as a result, wearing feel may be deteriorated. The moisture content is almost in a proportional relationship with a coefficient (i.e., linear swelling coefficient) representing the degree of change in size between the state prior to moisturization of the hydrogel (i.e., xerogel) and the state after swelling to reach equilibrium by absorbing the moisture. Therefore, reduction of the linear swelling coefficient in water as low as possible leads to decrease in the moisture content of the hydrogel. Accordingly, an ophthalmic lens having a low linear swelling coefficient, and is capable of achieving comfortable wearing feel for a long period of time has been demanded.
Contact lenses having antibacterial properties are disclosed in, for example, Japanese Unexamined Patent Application, Publication No. H4-76518. The antibacterial contact lenses are produced by kneading an antibacterial ceramic carrying a metal selected from silver, zinc and copper into a base material such as a hydrogel, or by coating a base material with an antibacterial ceramic, thereby imparting an antibacterial property to the contact lens. This antibacterial effect is exerted by generation of active oxygen due to the silver, zinc or copper metal, followed by killing of common bacteria and mold by the generated active oxygen. However, such a contact lens is disadvantageous in that use for a long period of time leads to impairment of the antibacterial property with time, as a result of elution or detachment of the antibacterial ceramic or the metal carried. In addition, Japanese Unexamined Patent Application, Publication No. H4-76518 does not disclose means for reducing the linear swelling coefficient of the contact lens in water.
Furthermore, for example, Japanese Unexamined Patent Application, Publication No. H6-337378 discloses a hydrogel that includes a copolymer obtained from a monomer mixture containing a hydrocarbon-group-containing (meth)acrylate having a hydroxyl group and may have an in-chain ether linkage, and a monomer having a quaternary ammonium salt in the side chain, as well as a soft contact lens formed from this hydrogel. However, although this hydrogel has a certain level of antibacterial properties per se, due to having very high hydrophilicity, when a cationic monomer such as a quaternary ammonium salt having a halide ion as a counter ion is copolymerized with other additional hydrophilic monomer to produce a hydrogel results in a too great linear swelling coefficient, thereby leading to failure in solving the foregoing problems. In addition, when the solubility of the employed monomers with one another is insufficient, and a hydrophobic compound must be further added to a system of copolymerization of a hydrophilic monomer with a monomer having a quaternary ammonium salt, in particular, the transparency is unsatisfactory. Moreover, Japanese Unexamined Patent Application, Publication No. H6-337378 does not disclose means for reducing the linear swelling coefficient when this hydrogel is used for an ophthalmic lens.
On the other hand, for example, Japanese Unexamined Patent Application, Publication No. 2008-122937 discloses an ophthalmic lens having a base layer part made of a silicone hydrogel containing a silicone component, and a superficial layer part made of a polymer compound including monomer units having at least one ammonium group in the molecule. Also, it is described that such an ophthalmic lens has an antibacterial property, and the antibacterial property is not reduced even if washing with water or the like is carried out. However, since this ophthalmic lens has a two-layer structure including a base layer part and a superficial layer part, it is manufactured by producing the base layer part first, and then forming the superficial layer part on the surface thereof. Therefore, multiple steps are included in manufacture, and thus the manufacture equipment becomes complicated, thereby leading to increase in the cost. Also, Japanese Unexamined Patent Application, Publication No. 2008-122937 does not disclose means for reducing the linear swelling coefficient of a contact lens.
Therefore, development of an ophthalmic lens having sufficient antibacterial property that is persistent even if used for a long period of time and also having practical transparency, with a low linear swelling coefficient in water has been strongly desired, which is capable of providing comfortable wearing feel and which can be easily manufactured.